1. Field of the Invention
The present invention relates to a fluid storage and dispensing system including dynamic monitoring of inventory of a fluid storage and dispensing vessel.
2. Description of the Related Art
In the field of semiconductor manufacturing, involving unit operations such as ion implantation, chemical vapor deposition, spin-on coating, etching, cleaning of process chambers, treatment of effluents, etc., it is common to utilize specialized fluid reagents of widely varying character.
Due to the high costs, significant toxicity, and ultra-high purity requirements of many of such fluid reagents, a variety of dedicated source vessels and containment apparatus have come into widespread usage in semiconductor manufacturing facilities. In many instances, these specialty fluid supply apparatus, which have replaced conventional gas cylinders in such service, are accessorized with various fluid monitoring and control devices. Such devices may for example include leak detection monitors, pressure transducers in dispensing lines, temperature sensors for ensuring that contained and dispensed fluid is at an appropriate thermal state for the associated process operation, mass flow controllers, restricted flow orifice elements, and the like.
Among the most innovative and commercially successful of the current generation of fluid storage and dispensing systems for semiconductor manufacturing reagents are those commercialized by ATMI, Inc. (Danbury, Conn.) under the trademarks SDS® and VAC®.
The SDS® fluid storage and dispensing system includes a vessel containing a solid-phase sorbent material having sorptive affinity for the semiconductor manufacturing fluid reagent, whereby fluid stored in the vessel on such sorbent material can be selectively desorbed therefrom and dispensed from the vessel under dispensing conditions. The semiconductor reagent fluid can be stored at low pressure as a result of its sorptive retention in the vessel, e.g., at subatmospheric pressures. As a result of such low pressure storage, a high level of safety is provided, in relation to high pressure gas cylinders in which a valve head failure can result in widespread dissemination of the fluid contents of the cylinder. The SDS® fluid storage and dispensing system is variously described in U.S. Pat. Nos. 5,518,528; 5,704,965; 5,704,967; and 5,707,424.
The VAC® fluid storage and dispensing system includes a vessel containing a semiconductor manufacturing fluid reagent and equipped with a pressure regulator that is interiorly disposed in the vessel and in flow communication with a dispensing assembly for dispensing of fluid at pressure determined by the set point of the pressure regulator. The pressure regulator set point can be set to a low dispensing pressure level. The VAC® fluid storage and dispensing system is variously described in U.S. Pat. Nos. 6,101,816; 6,089,027; 6,360,546; 6,474,076; and 6,343,476.
By its interior pressure regulator configuration, the VAC® fluid storage and dispensing system achieves an enhancement of safety in the containment of high pressure fluids, since the regulator prevents the discharge of fluid at pressure above the regulator set point, and since the regulator is inside the vessel and thereby protected from ambient contamination and direct impact.
In ion implant applications, the SDS® fluid storage and dispensing system has become a standard gas source in the semiconductor manufacturing industry. Currently, it is estimated that approximately 80% of the installed base of 4000 ion implant units worldwide utilize the SDS® fluid storage and dispensing system.
In order to assure proper utilization of the SDS® fluid storage and dispensing system, special consideration of the gas delivery system design including low pressure drop components and accurate measurement of sub-atmospheric (torr-level) pressure is required. This poses a particular problem in that there are a half dozen or so major manufacturers of ion implant equipment. Each manufacturer makes several model types and new products are released every 2-3 years. This circumstance results in a wide variety of ion implant systems and subsequently results in a myriad of gas monitoring techniques being in use, many of which are inadequate or otherwise inefficient and unstandardized.
In one of the most popular current ion implant system designs, gas monitoring of the inventory of fluid in the SDS® fluid storage and dispensing system requires navigating through a complex series of software files in order to determine pressure of the fluid in the SDS® fluid storage and dispensing vessel. The user then has to manually convert the pressure into a unit of fluid utilization. The problem with this approach is that the time required to navigate the software screens in this implementation is excessive, and most ion implant operators and technicians cannot understand the conversion mathematics required to convert the pressure reading into a meaningful utilization expression.
The foregoing deficiencies in monitoring utilization of fluid stored for dispensing in the fluid supply vessel is exacerbated by the fact that numerous implanter units, e.g., 5-20, are provided in a typically-sized semiconductor manufacturing facility, or “fab.” The multiplicity of such units means that it often requires an operator or technician to spend hours in monitoring operations for all of the implanter units to determine the rate and extent of fluid consumption by the ion implanter, or other dispensed fluid-using equipment in the semiconductor fab.
Another problem with conventional approaches to monitoring fluid utilization for determining consumption of the fluid in the fluid supply vessel is that it is difficult to predict and alert fab personnel to the approaching end-point of the dispensing operation, when the vessel is nearly depleted of its fluid contents and approaching exhaustion.
Since existing approaches to determination of utilization are poor, it is a not infrequent occurrence that fab personnel run out of fluid without warning during active implant operation. This occurrence typically has a severe impact on fab productivity since the implant unit must then be shut down to accommodate change-out of the depleted fluid supply and dispensing vessel, and installation of a fresh vessel containing fluid for renewed operation. Since this occurrence is unscheduled, the efficiency with which the fluid storage and dispensing system can be replaced is less than if the event were scheduled or able to be predicted.
Another issue related to use of materials in semiconductor manufacturing relates to their cost. The prices of many specialty materials for semiconductor manufacturing are in a range of from $10-$200 US per gram and the packaging volumes of many specialty chemicals continues to increase due to higher consumption rates for larger wafer semiconductor process tools, e.g., 300 mm wafers and higher diameter wafers.
In consequence, consumers of specialty materials are often forced to purchase needed volumes of such materials at unit prices that often exceed their internally defined thresholds for capital purchases. Under Generally Accepted Accounting Principles in the United States (US GAAP), material purchases must be expensed at the time of purchase, so that purchasers expense the entire volume of purchased specialty chemical before using same in their material-utilizing processes. This is a significant operational cost burden on semiconductor manufacturing facilities.
There is therefore a significant need in the art for a fast, accurate and reliable approach to monitoring utilization and detecting end-point dispensing conditions in the use of fluid storage and dispensing systems of the above-described type.
There is concurrently a need for easing the operational cost burden on semiconductor manufacturing facilities deriving from the aforementioned accounting requirements of US GAAP for expensing entire volumes of purchased specialty chemicals for use in semiconductor manufacturing operations.